Piles, usually made out of concrete, are generally used to form the foundations of buildings or other large structures. A pile can be considered a rigid or a flexible pile. Typically a short pile exhibits rigid behavior and a long pile exhibits flexible behavior. The criteria for rigid and flexible behavior depend on the relative stiffness of a pile with respect to the soil and are known in the art. The purpose of a pile foundation is to transfer and distribute load. Piles can be inserted or constructed by a wide variety of methods, including, but not limited to, impact driving, jacking, or other pushing, pressure (as in augercast piles) or impact injection, and poured in place, with and without various types of reinforcement, and in any combination. A wide range of pile types can be used depending on the soil type and structural requirements of a building or other large structure. Examples of pile types include wood, steel pipe piles, precast concrete piles, and cast-in-place concrete piles, also known as bored piles, augercast piles, or drilled shafts. Augercast piles are a common form of bored piles in which a hollow auger is drilled into the ground and then retracted with the aid of pressure-injected cementatious grout at the bottom end, so as to leave a roughly cylindrical column of grout in the ground, into which any required steel reinforcement is lowered. When the grout sets the pile is complete. Piles may be parallel sided or tapered. Steel pipe piles can be driven into the ground. The steel pipe piles can then be filled with concrete or left unfilled. Precast concrete piles can be driven into the ground. Often the precast concrete is prestressed to withstand driving and handling stresses. Cast-in-place concrete piles can be formed as shafts of concrete cast in thin shell pipes that have been driven into the ground. For the bored piles, a shaft can be bored into the ground and then filled with reinforcement and concrete. A casing can be inserted in the shaft before filling with concrete to form a cased pile. The bored piles, cased and uncased, and augercast, can be considered non-displacement piles.
Often a pile is constructed to withstand various external lateral and eccentric loads. The external lateral and eccentric loads can result from high winds, rough waves or currents in a body of water, earthquakes, strikes by one or more large masses, and other external forces. The external lateral forces on structures can induce moments, which the foundations must resist. If the foundation incorporates piles, some of the piles can experience additional compression and others reduced compression or tension to supply the required additional moment resistance. Typically axial load testing or other axial capacity correlations are performed to design a pile capacity. Often the additional moment resistance requires additional pile size, pile length, and/or pile number.